1. Field of the Invention
The present invention relates to an ignition apparatus for an internal combustion engine arranged such that a power switch for intermittently feeding a primary current to an ignition coil and a primary coil and a secondary coil of the ignition coil are contained in an insulation case and the power switch, the primary coil and the secondary coil are fixed by an insulating resin material poured into the insulation case.
2. Description of the Related Art
FIG. 11 is an overall perspective view of a conventional ignition apparatus for internal combustion engine disclosed in Japanese Utility Model Laid-Open No. 4-77220, FIG. 12 is a longitudinal sectional view of the ignition apparatus of FIG. 11, FIG. 13 is a perspective view of an insulation case of FIG. 11 and FIG. 14 is an electric circuit diagram of the ignition apparatus for internal combustion engine. In the drawings, a hole 1b is defined in the bottom of the accommodating section 1a of a synthetic resin insulation case 1 at the center thereof. The central portion of a first E-shaped iron core 2 of an ignition coil extends through the hole 1b. A second E-shaped iron core 3 of the ignition coil is spaced apart from the first E-shaped iron core 2 in confrontation therewith. A primary coil 5 is wound on a bobbin 4 around the central portions of the first and second iron cores 2,3. The ignition coil has a secondary coil 6 wound around the outer periphery of the primary coil 5 thereof.
A power switch 7 is accommodated in an auxiliary accommodating section 1c projecting from the accommodating section 1a. The power switch 7 includes a tray-shaped iron metal case 8, a switching device 9 composed of a power transistor accommodated in the metal case 8, a hybrid integrated circuit (hybrid IC) 10 for driving and controlling the switching device 9, a silicon gel 11 filled into the metal case 8 for protecting the switching device 9 and the hybrid integrated circuit 10, and a lid 12 for sealing the interior of the metal case 8.
The insulation case 1 includes a holding section for a high-tension terminal 13 and a holding section 1e for a low-tension terminal section 14. The low-tension terminal section 14 includes a first low-tension terminal 14a for connecting the primary coil 5 to the battery of an automobile, a second low-tension terminal 14b for imposing an ignition signal from a control unit (not shown) on the power switch 7, and a third ground low-tension terminal 14c. Note, the accommodating section 1a and auxiliary accommodating section 1c of the insulation case 1 are filled with an insulating resin material 15 which may be cured epoxy resin.
In the ignition apparatus for the internal combustion engine arranged as described above, a primary current flowing to the primary coil 5 of the ignition coil is controlled through the power switch 7 in response to an ignition signal which is input from the second low-tension terminal 14b through the control unit. A high-tension voltage is generated to the secondary coil 6 of the ignition coil in accordance with the primary current flowing to the primary coil 5 and fed to a distributor (not shown).
In this example, the metal case 8 is used to secure the heat radiation property of the power switch 7 and powder of alumina or the like having a good thermal conductivity is contained in the insulating resin material 15 so that heat generated from the power switch 7 is uniformly diffused to the overall metal case 8 and discharged to the outside air through the insulating material 15 and insulation case 1.
In the conventional ignition apparatus for the internal combustion engine, heat generated by the operation of the power switch 7 is liable to be radiated to the outside by the radiating action of the metal case 8. However, when heat generated by the operation of the ignition coil is discharged to the outside air through the overall surface of the insulation case 1, a problem arises in that the power switch 7 located in an intermediate portion of heat path is affected by the heat from the ignition coil and the temperature thereof is increased. As a result, the power switch 7 may malfunction.